US2114738A - Carbon pigment producing furnace - Google Patents

Description

FFHCE UNITED STATES PTEN'E' il',

CARBON PIGMENT PRODUCING FURNACE George L. Heller, Pampa, Tex., and Harold M. Wilgus, Merrick, N. Y., assignors to General Atlas Carbon Company, Dover, Dei., a corporation of Delaware Application June 19, 1937, Serial No. 149,056

8 Claims. (Cl. 134-60) This invention relates to the manufacture of lating the thickness of the air and gas sheets. carbon pigments, and is particularly directed to and their relative volumes and velocity rates so an improved design of carbon pigment producas to cause them to ow in contacting relation ing furnace. The carbon pigment producing Without substantial turbulence throughout the furnace which forms the subject of the present length of each reaction chamber. The streams of 5 invention represents an improved design of our gas and air enter each reaction chamber through furnace as disclosed in the copending process a plurality of superimposed narrow alternate air application of George L'. Heller and Carl W. and gas burner slots or ducts, and the velocities Snow, Serial No. 87,657, filed June 27, 1936, of the respective gas and airstreams are preferl0 Likewise the furnace of the present invention ably substantially equal as they enter the rel0 represents an improvement on the carbon pigaction chamber. Under these conditions mixing ment furnace which is described in the United 0f the gas and ail OCCulS Within the reaCiiOIl States patent of David J. Beaver, No. 1,902,753, Chamber substantially solely7 aS e result 0f difgranted March 21, 1933. fusion, so that conditions favorable for combus- The process inventions of the Beaver patent tion only occur at the interface between the gas l5 and of the Heller and Snow application above and air Streams. referred to are based on the discovery that car-l Under the Conditions 0f preferred Operation bonaceous pigments can be produced in high which the present furnace is designed to promote, yield by partial, secondary combustion of natthe high temperatures Which develop by Partial ural gas within a combustion chamber into combustion at the interfaces of the gas and air which the gas and air are directed in a plurality streams cause thermal reactions of the gas Withof alternate thin, wide contacting sheets, while in the ame envelope Surrounding each gas thin viscous flame fronts are formed and main- Stream. Such thermal TeaCtiOIlS PlOdilCe finely tained around each sheet of gas as the gas divided solid hydrocarbon particles which are carand air move forwardly through the combustion fied along by the eas Within a viscous gaseous en- 25 chamber in parallel streamline non-turbu1ent VeiOpe 0f 110i? COmbIlStiOn gases. The maier P01- ow relation out of contact with solid or liquid i'fiOIl 0f the heat required fOl raising the temsurfaces. perature above that at which dissociation of the The present invention has among its primary gas occurs is transmitted by radiation directly objects to provide an improved carbon pigment from each luminous flame to the ges Streams 0I' 30 producing furnace which is designed on the same Sheets behind adjacent flamesbasic principle as the furnace of the aforemen- Each ges Stream iS entirely Surrounded by an tioned Beaver patent, the improvements in deail Stream and by 'COmbuS'Ciei gases during its sign being directed toward more eflicient conpassage through the react/10h Chamber and the version of the natural gas 0r other hydrocarbon furnace is designed so that the total cross sec- 35 gas into a marketable finely divided Carbon tional area of each chamber is substantially equal product, and the more efficient protection of the to the total cross sectional areas of the combined product as originally formed against deterioraair and gelsv Streams et the pOiIll' Where4 Such tion by harmful secondary reactl0nsstreams first contact on entering the combustion 40 With the above objects in mind one feature chamber. The furnace design is directed toward'40 of the invention contemplates va, furnace chaminsuring substantially streamline iiow of; the gas ber having its longest axis disposed in a Suband air streams out of Contact with any surface stantielly horizontal plane, and having its forwhich might have an inhibiting or anti-catalyst ward portion partitioned into a plurality of rela-A effect Orl recovery Of maximum yields 0f high tively deep and narrowreaction chambers of quality eelbOn Pigmente 45 uniform unobstructed cross section all communi- With the aboveand other objects and features cabiy connecting with a single large unobstructin view, the invention resides in the improved ed mixing and blending chamber in the rearcarbon pigment ful-nace which is hereinafter deward portion of the furnace. The improved described and more particularly denned by the 5o sign further provides for introducing natural accompanying ClaimS- 50 gas or other hydrocarbon gas and sufiicient air In the following description of the invention for developing reaction temperatures by partial reference will be made to the accompanying combustion, in a plurality of alternate thin 'con-v drawing, in which: tacting parallel streams or sheets into the for- Fig. 1 is a vertical section through a furnace 66 ward end of each reaction chamber, and for reguembodying improved Ldesign features of the present invention, certain parts of the furnace, particularly the burners, being shown out of scale in order to better illustrate the design;

Fig. 2 is a horizontal cross section through the funiace taken along the plane 2-2 of Fig. 1; and

Fig. 3 is an enlarged view in vertical elevation l row individual reaction chambers I6 each hav-` ing its major axis horizontal. At the forward end of each reaction chamber I6 there is mounted a burner element I8 which is supported at the front wall of the furnace and forms a closure for the front end of the corresponding reaction chamber I6. Each burner element I8 is provided with a metal casing 20 which is contoured and dimensioned to t the front end of one of the reaction .chambers I6 and which is attached to the front wall of the furnace by flanges 2|. These burner elements I8 serve as hydrocarbon gas and air supply ducts for the furnace and are disposed on the front wall of the furnace to afford ease of access for purposes of rapid removal, cleaning, replacement, and to dissipate radiant heat which is transmitted to the burner.

The natural gas or other hydrocarbon gas which is to be dissociated in the furnace for the production of carbon pigmentsis introduced to each ofthe burners I8 through an individual valve controlled gas supply pipe 22. Air for supporting secondary combustion of the gas Within the furnace is conducted'to each of the burners through individual air supply pipes 24 past air flow control dampers 26. Pressure regulating valves and ow meters (not shown) are connected in the main gas and air supply pipes to assist the operator in maintaining the desired ratio of gas and air.

Within the burner elements I8 the individual gas supply pipes 22 are each enclosed by a vertical gas supply manifold 28 which is conveniently constructed in the form of a rectangular box. Manifold 28 forms a partof the gas burner, and the portion of the corresponding gas feed pipe 22 which lies within the manifold is drilled with tw`o rows of small apertures 30 (about ya diameter) which face at an angle towardthe back of the burner. apertures 30 is preferably only about 75% of the cross sectional area of the pipe 22, so that as the gas is supplied to the pipe 22 under low pressure the apertures 38 form a series of small orifices which distribute the gas evenly throughout the length of manifold 28. As the gas exits through the apertures 30 into the manifold it impinges on the back of the manifold and its direction of flow is reversed toward the front of the furnace, the gas passing from the manifold 28 into a plurality of spaced superimposedgas burner ducts 32.' Each burner duct forms the gas into a thin wide sheet in which form the gas issues lfrom each burner tip 34. In one operating furnace the burner is built up of a large number (34) of gas ducts having chrome steel tips about y, inch thick and 81/2 inches wide (inside dimensions), such ducts being uniformly spaced about 1 inch apart and discharging into a reaction chamber I8 the major dimensions of which The total cross sectional area of the.

are: width 12 inches, height as inches, and length 6 feet 9 inches.

Each of the burner ducts 82 is constructed of a pair of uniformly spaced horizontally disposed chrome steel platesor vanes 35. The upper vane tapers in width (for example) from a full 8% inch width of the burner at the vertical plane of the burner tip, to an approximately 4 inch width at the vertical plane at which the plates are attached to the front end of the gas distributor box 28. The upper one of each pair of plates is provided with a spacing angle 38 by which it is attached to the front of the manifold 28, and by which the upper plate of each burner duct is spaced from the lower plate of the adjacent overlying burner duct. The gas exit end of each burner duct has a width which may vary within limits of 2 inches to 4 inches less than the width of the corresponding combustion chamber I6. The lower plate of each burner duct has a width corresponding to the Width of the burner casing 20 to which the edges of the plate are attached, so that each pair of adjacent lower burner to high temperatures, and accordingly must be constructed so as to withstand such high temperatures without warping or oxidation and without catalytic effect on the decomposition of the gaseous hydrocarbon which is introduced to the furnace. therethrough. A high chromium steel or alloy of chromium and iron containing 25% or more of chromium and less than of iron, has proved to be a suitable material for use in constructing the burner tips, and an alloy of lower chromium content (12%) may be used for the burner vane construction. Other high temperature alloys may be used in constructing the burner tips, such for .example as alloys of iron and tungsten, manganese and vanadium containing less than 75% iron and substantially no nickel, copper or silicon. 'I'he burner tips are secured to` the burner vanes by socket or welded joints indicated by the numerical designation 40.

The air supply for supporting partial combustion of the gas enters the furnace from the feed line 24 throughan air distributor manifold 42 which consists of a cylindrical pipe mounted eccentrically in a half round casing 44. The forward end of casing 44 is attached to the burner casing 20 by a flange 46. Air supply manifold 42 receives air under the pressure of a rotary blower or other source of low pressure air (not shown) and distributes the air uniformly throughout the height of the casing 44 through slots 48 which are cut in the rear wall of the manlfold. Slots 48 are uniformly dimensionedas to area, but are made gradually narrower and longer in direct ratio to the distance separating the slot from the inlet of manifold 42. Bailles 50 are placed within manifold 42 behind each slot 48 for the purpose of intercepting the air entering the manifold and deilecting it outwardly through the slotsl to the rear wall of casing 44, by which the direction of air flow is reversed and the air is thereby distributed uniformly to the air ducts 38 throughout the full height of com,-

bustion-chamber I6. The areas of the baffles 50 vary directly with the distance separating them from the inlet port of manifold 42. In one design such baffle area variation ranges from 1/th through 1/5'tb, 1Ath, 1/3rd, l/2 to 1 of the total inside area of the manifold 42.

As the air ows forwardly from the rounded rear end of air casing 44 toward the burner air ducts 38 some of it passes through a restriction 52 (Flg..2) which is positioned forwardly of the gas distributor box 28 in about the vertical plane of the flange 4B of the burner casing. This restriction further promotes uniform distribution of the air to all parts of the burner, and insures that the air flows in equal volume and at equal velocity into the air ducts 38, Where any turbulence is smoothed out before the air passes beyond the vertical plane of the burner tips. The inside face of the flange 2| is shown in Figs. 1 and 2 as protected by a refractory shield 54 in and adjacent the vertical plane of the burner tip, this shield 54 forming in effect an extension of the inner walls of reaction chamber I6 rearwardly of the burner tip. The insideside wall surface of the shield 54 tapers in'a direction away from the burner tip and away from a restriction 55 in the plane of the burner tips. This construction assists in inhibiting the development of turbulence in the gasand air sheets issuing from the burner into the reaction chamber, and also permits a certain amount of wall expansionl in the zone of the burner tip Without interference with the symmetry of the ames issuing from the burner.

The reaction chambers I6 are proportioned as to length in accordance With the volume of hydrocarbon which is reacted, so as to insure conversion of the gaseous hydrocarbon to a solid, finely-divided product during the period in which the gas, emitted from the burners, traverses the length of the reaction chamber. vThe length of each reaction chamber in a commercial furnace lies within the range 5 -ft.7 ft., and the width in the range 8 inches-12 inches.

The mixture of `products of combustion laden with carbon pigment which is produced in each of the reaction chambers discharges into a common large mixing and blending chamber 5B .occupying the rear portion of the furnace Ill,

from which the mixture of gases is led off through an air cooled offtake pipe. 58. After traversing the offtake pipe 58 the gases are further cooled by Water quenching, and the carbonaceous pigment vis separated therefrom by electrical precipitators or other separating means (not shown). The design of the blending chamber 56 is such as to insure travel of the gases laden with pigment throughout the length thereof Without substantialv reduction of velocity, but with the development of turbulence which inhibits accretion or particle growth. An arched roof 60 is provided for 'the blending chamber 56 to assist in retention of radiant energy Within the reaction chambers I6, and to insure against substantial reduction in flow rate of the gases in traversing the furnace from the burner tip to the inlet of offtake 53. In one such furnace the total distance from the burner tips to the inlet end of pipe 58 is approximately' 12 feet.

As the gas travels forward from a burner tip.

. gas sheet or stream diffuses more 'rapidly than the hydrocarbon into the air stream or air blanket surrounding the gas stream. By following the streamline method of combustion the hot burning gases within each flame front have a comparatively high viscosity, so that the nely divided solid carbon and/or hydrocarbons which are formed by the heat developed within the gas stream inside of the :dame front are substantially all held against the inner face of the viscous flame, and pass forwardly through the furnace into the blending chamber 56 in a definite non-turbulent or streamline path without coming in contact with solid surfaces. By this method of operation the finely divided solid is carried in suspension rapidly through the high temperature reaction zone without becoming oxidized and without becoming graphitized by contact With solid surface or by too long exposure to high temperatures.

Because of the high temperatures which are developed within the furnace, and particularly within the reaction chambers IG, it is necessary to employ refractory containing a high percentage of alumina or other high temperature resistant refractory material, particularly in the zones of the furnace exposed to the highest temperatures. To minimize expansion and contraction stresses and destruction and disintegration of the refractory by spalling, the furnace is preferably constructed of gradedrefractory arranged in such a way that the roof of the blending chamber 56 and the end sections of the partitions id and floor which lie adjacent to the blending chamber 56 are preferably constructed of refractory brick containing upwards of 70% alumina, while the remainder of the floor, side and rear walls and the inner linings of the forepart of the reaction chambers I6 are constructed of alumina brick containing alumina in the proportion ofy about 60%. These linings are backed up with brick work of good heat insulating properties, and the whole furnace structure is designed to minimize development of stresses in the brickwork and steel casing, and to allow for ample expansion without disintegration or spalling. Variations in expansion stresses are equalized by ,grading the bricks as to their alumina content substantially in direct proportion to the temperatures to which they are exposed within the furnace.

The furnace incorporates another feature which adds to the eiiiciency of operation and the life of the furnace, and that is the provision for simultaneously air cooling the floor, walls and roof of the furnace while preheating the air sup'- plied for supporting partial, secondary combustion within the furnace, thereby increasing the heat utilization eiciency of the carbon pigment production for which the furnace is designed.

The circuit followed by the air supply through the furnace is indicated in Figs. 1 and 2 as including a main air supply pipe 10 which conducts the air from a blower or other source of dinal channels extending throughout the length ofthe furnace beneath the floor, being distributed from the manifold I2 uniformly through each of the passages 'I3 by means of control dampers M located at the inlet end of each passage 'l3. The air flows through the passages toward the back wall of the furnace, and the channels separating the passages are provided with apertures 'I6 through which the air iiows and is directed by bames 1l outwardly toward upright passages 18 in the side and back walls of the furnace, through which the air is conducted into other passages 80 built into ythe roof of the furnace.

After entering adistributing manifold l2 overlying the front portion of the furnace, part of the preheated air passes through pipes 84 into pipes 2l supplying air to each of the upper set of burners I8, while additional preheated air iiows downwardly through down passages 86 in front side wall of the furnace and thence through pipes 88 into pipes 24 supplying the lower rows of burner elements I8. Each of the burner elements is supplied with air in amount which is controlled by the calibrated dampers 26 in the individual air supply ducts 24.

The individual burner ducts 32 are sized within optimum limits of 1;-1/2 inch thickness, and 6 inches to 10 inches width (inside dimensions). The ratio of the total cross sectional inner perimeter of the burner ducts to their total inner cross sectional area at their outlet ends lies in the range 4 to 11. When supplying ordinary natural gas of a heating value of about 1000 B. t. u./cu. ft. to the furnace for conversion to a nely divided carbonaceous rubber reenforcing pigment, the optimum cross sectional area ratio of burner air ducts to gas ducts is about 4.5. Depending on the gas being handled, this ratio may be varied within limits to supply sumcient air to burn 30% to 80% of the gas.

The furnace is constructed for operation within temperature limits of 2000-2800" F. The use of multiple thin narrow wide burners is an important feature of the construction whereby carbonaceous pigment is produced within thin broad and fiat flames, thereby insuring formation of a maximum amount of solid carbon or hydrocarbon within each iiame through activation by direct radiation from other flames. The hydrocarbon gas thereby forms the raw`materia1 for production purposes and also the source of energy for the conversion.

The invention having been thus described,-

what is claimed as new is:

1. Apparatus adapted for producing carbon pigment from gaseous hydrocarbons by partial secondary combustion comprising, a furnace chamber with refractory heat insulating floor, side walls and roof and having an unobstructed gas blending chamber in its rearward interior portion and a plurality of refractory partitions in its forward portion, said partitions forming individual unobstructed reaction chambers each substantially uniform in cross section throughout its length and each communicating at its rearward end with the blending chamber,.un insulated gas burner umts each of substantially the same cross sectional area as a reaction chamber and each comprising a plurality of uniformly spaced horizontally disposed narrow gas ducts mounted in parallel Isuperposed rows at the for- "vard end of each reaction chamber and connected with a common source of gas. together with air ducts surrounding each of the gas ducts and connected with a common source of air, and a large refractory lined gas offtake pipe leading of! horizontally from the rearward end of the blending chamber.

2. Apparatus as defined in claim 1 together with communicably connecting air passagesin the floor, side walls and roof of the furnace', and

means for distributing air which has preheated in said passages at a controlled rate to each gas burner air duct.

3. Apparatus as defined in claim 1 in which the refractory linings of the furnace and the partition walls comprise high alumina brick gradedl in its alumina content in accordance with vvariations intemperature at different parts of the furnace to minimize expansion stresses.

4. Apparatus as defined in claim 1 in which the gas burner units form closures for the forward end of each reaction chamber and are housed in a metal casing conforming closely in contour with the surrounding walls of the reaction chamber and attached thereto by anges, which flanges are in turn protected interioriy by a refractory shield having an inner. wall which outlet ends is normally about 1:4.5 and is proportioned to supply s uillcient air to burn 30% to.80% of the gas.

6. Apparatus as dened in claim l in which each gas burner embodies at its forward end an air distributor comprising a semi-cylindrical casing which communicably connects with the gas burner air ducts, a cylindrical air supply conduit mounted eccentrically in the casing and provided with uniformly spaced rear wall slots of equal area and battles behind each slot having areas which vary directly with their distance away from the inlet end of the conduit, wherebyto deiiect incoming air through the slots and against the rounded end of the casing at a rate which is substantially uniform throughout the length of the casing.

7. Apparatus as deflned in claim 1 in which each burner duct is provided with a high temperature resistant burner tip comprising an alloy consisting of at least chromium and less than 75% of iron by weight.

8. Apparatus as dened in claim 1 in which each of the gas burner ducts has a uniform thickness in the range 1, inch-one-half inch, and

in which each of the combustion chambers has a width of approximately 8 inches-12 inches and a length of about 5 ft.-7 ft.

f GEORGE L. KELLER.

HAROLD M. WILGUB.

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